Keyer-synthesizer for an electronic musical instrument employing an integrated circuit



w. c. RING 3,534,144 KEYER-SYNTHESIZER FOR AN ELECTRONIC MUSICAL INSTRUMENT AN INTEGRATED CIRCUIT Oct. 13, '1970 'I EMPLOYING Filed Janj.

2 Sheets-Sheet 1 Oct. 13, 1970 w. c. RING 3,534,144 KEYER-SYNTHESIZER FOR AN ELECTRONIC MUSICAL INSTRUMENT EMPLOYING' AN INTEGRATED CIRCUIT Filed Jan. 2, 1969 Z'Sheets-Sheet 2 f Zar 205 @D 20c 205 204 21N 1401" /WE 1400 1406 F405 1404 a, C. M, JM Pgf/MM I @s United States Patent O 3,534,144 KEYER-SYNTHESIZER FOR AN ELECTRONIC MUSICAL INSTRUMENT EMPLOYING AN IN- TEGRATED CIRCUIT William C. Ring, Carpentersville, Ill., assignor to Hammond Corporation, Deerleld, Ill., a corporation of Delaware Filed Jan. 2, 1969, Ser. No. 788,407 Int. Cl. Gh 1/00 U.S. Cl. 84-1.01 8 Claims ABSTRACT OF THE DISCLOSURE A combined keyer-synthesizer for synthesizing stairstep-sawtooth electrical output signals from a plurality of harmonically related square wave signals in response to the actuation of key switches is disclosed. The keyersynthesizer, which finds major application in electronic musical instruments such as the electric organ, employs an integrated circuit having a control input, for controlling one or more transfer circuits which have a plurality of input terminals -for related harmonics and one or more output terminals for complex signals which are a scaled synthesis of certain of the input signals. In one version the synthesizer employs MOSFET dynamic circuit elements. In another embodiment it employs a multi-emitter transistor as its dynamic circuit element.

FIELD OF THE INVENTION The present invention is directed toward a new and improved keyer-synthesizer system for electrical musical instruments and to a unique keyer-synthesizer unit which forms a portion of the system.

One form of electric organ provides all needed notes of the musical scale to satisfy the compass of the instrument in the form of square wave signals. Square waves are deficient in harmonic structure, particularly in even harmonics, and so various schemes have in the past been provided for obtaining bright waves, sometimes referred to as sawtooth waves or unsymmetrical waves, from the square wave sources. A common approach is to add carefully scaled octavely related square waves so that the synthesized stairstep wave thus produced approximates a sawtooth. This invention is concerned with this scheme but is an improvement over the usual arrangement and reduces the cost and insures greater precision in the scaling. In addition, the mechanism for keying the signals into the organ output system is integrated into the synthesizing circuits.

SUMMARY OF THE INVENTION One feature of the present invention is the provision of a keyer-synthesizer for synthesizing an electrical output signal from a plurality of electrical input signals. This keyer-synthesizer comprises semiconductor means which has a common gate and a common output but a plurality of inputs. The gate controls the current flow between the plurality of inputs and the output. The inputs are individually coupled to one of the plurality of input signals. When the gate is coupled to a predetermined keying signal, current flows from the plurality of inputs, through the semiconductor means, to the output thereby producing an output signal that is a synthesis of the various inputs.

Another feature of the invention involves a keyingsynthesizing unit in which a plurality of such keyer-synthesizers are coupled to a plurality of input signals and to at least one keying input. The unit includes one output for each keyer-synthesizer and functions to synthesize at least two different output signals in response to the keyer.

A further feature of the invention is the combination Mice of such a unit in an electronic musical instrument which includes a source of a plurality of square wave signals of different frequencies, key switches, keying response selector circuits coupled therewith and conventional musical signal altering, mixing and amplifying circuits for driving one or more speakers. The unit is coupled to the square wave source and synthesizes, in response to the closure of one of the key switches, a stairstep-sawtooth waveform of various components at one or more of its outputs. The output of the unit are coupled to the conventional electronic musical instrument circuits so that one or more musical tones, derived therefrom, are sounded. The keying response circuit includes response selector means whereby the rates of attack and decay of the synthesized output signals and thus the rates of the sounded musical tones are selectively varied.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in the several iigures of which like reference numerals identify like elements, and in which:

FIG. l is a schematic circuit diagram of an electronic musical instrument of the organ type including a keying and synthesizing unit incorporating the principles of the present invention;

FIG. 2 is a schematic circuit diagram of a keyer-synthesizer portion of the unit of FIG. l, also constructed in accordance with the principles of the present invention;

FIG. 3 is a schematic circuit diagram of an alternative construction of the keyer-synthesizer portion of the unit of FIG. l, also constructed in accordance with the principles of the present invention; and

FIG. 4 is a schematic circuit diagram of a second keying and synthesizing unit of a modified construction incorporating the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 there is depicted a portion of an electronic musical instrument of the organ type which incorporates the principles of the present invention and is generally designated by the numeral 10. The electronic organ 10 includes a source 11 of a number of essentially equal amplitude square wave signals of differing frequencies.

In accordance with the present invention a stairstep sawtooth wave synthesizer unit 12 is coupled to outputs of source 11 to synthesize at particular ones of its output terminals, stairstep-sawtooth waveform signals in response to the closing of key switches, symbolized by the switches 8-2 and 83, of the organs playing keys and in a keying manner determined by keying selector circuits 17 and 19. The outputs of the synthesizing u'nit 12 are coupled to the conventional switching, alternating and amplifying circuits 18 of the organ 10 to be ultimately sounded by one or more speakers, such as the speaker 20.

The synthesizer unit 12, although generally termed herein a synthesizer, performs the dual functions of synthesizing and keying and is a combined synthesizer and keying unit. That is, it synthesizes a particular output signal only when a particular related key is depressed, thus eliminating the need for excess parts and eliminating the generation of unneeded signals.

More particularly, the synthesizing unit 12 includes six input terminals designated 20A, 20B, 20C, 20D, 20E and 20F. At each of these input terminals 20 a different square wave signal, such as that illustrated at 21 is delivered by the source 11. These signals vary at least in their frequency. The frequency of the waveform at the input terminal 20a is a fundamental note While that of terminal 20B is its second harmonic, that of terminal 20C is its fourth harmonic, that of terminal 20D is its eighth harmonic, that of terminal 20E is its sixteenth harmonic; and that of terminal 20F is its thirty-second harmonic. Representative values are as follows:

Terminal: Frequency, Hz. 20A 220 The periods of the signals are aligned, that is, whenever the fundamental frequency is keyed, each of its harmonics is also sounded along with it.

The signals impressed upon the terminals 20 are coupled to individual synthesizers designated 30A, 30B., 30C, 30D and 30E. Each of these synthesizers 30 is of essentially identical construction and operation as will be detailed with respect to the discussion below of FIG. 2. For the present it is sufficient to note that each of the synthesizers 30 has tive inputs 31, 32, 33, 34 and 35 and one output 36.

The input signal at the terminal 20A is coupled to the input 34 of the synthesizer 30A as illustrated by the line 59. Line 59 is also connected by a branch 58 to 34 of synthesizer 30D. The input terminal 20B is coupled, as illustrated by the line 52, to the input 33 of the synthesizer 30A. The terminal 20B is `further coupled, -as illustrated by the lines 55, 56 and 54, to the inputs 34, 33 and 34, respectively, of synthesizers 30B, 30D and 30E. The input terminal 20C is coupled to the input 32 of synthesizer 30A as indicated by the line 53. As further indicated by the lines 51, 49, 52 and 50 the input terminal 20C is also coupled to, respectively, the input 33 of the synthesizer 30B, the input 34 of the synthesizer 30C, the input 32 of the synthesizer 30D, and the input 33 of the synthesizer 30E.

The input terminal 20D of the unit 12 is coupled, as indicated bythe lines 48, 46, 44, 47 and 45 to, respectively, the input 31 of the synthesizer 30A, the input 32 of the synthesizer 30B, the input 33 of the synthesizer 30C, the input 31 of the synthesizer 30D', and the input 32 of the synthesizer 30E. As similarly indicated by the lines 43, `41, and 42, the input terminal 20E of the unit 12 is coupled to, respectively, the input 31 of the synthesizer 30B, the input 32 of the synthesizer 30C, and the input 31 of the synthesizer 30E.

The last of the square wave input terminals 20F is coupled, as indicated by the line 40 to the input 31 of the synthesizer 30C.

In the above described manner the synthesizers 30A and 30D are coupled to the input terminals 20A, 20B, 20C and 20D; the synthesizers 30B, 30C and 30E are coupled to terminals 20B, 20C, 20D and 20E; and the synthesizer 30C is coupled to terminals 20C, 20D, 20E and 20F The inputs 35 of the synthesizers 30A, 30B and 30C are, as indicated respectively by the lines 62, 61 and 60, coupled in common to a keying input terminal 65 of the unit 12. Similarly, the inputs 35 of the synthesizers 30D and 30E are, as indicated by the lines 68 and 67, connected in common to a keying input terminal 70 of the unit 12.

The outputs 36 of the five synthesizers 30A, 30B, 30C, 30D and 30E are respectively coupled, as indicated by the lines 75, 73, 71, 74 and 72 to individual ones of the I'ive output terminals 80, 78, 76, 79 and 77.

The keying input terminals 65 and 70 are each connected to one of the keying response selector circuits 17 or 19. As these circuits are identical in construction, only the circuit 17 will be described in detail. The selector circuits 17 and 19 respectively respond to a key switch symbolized by 82 and 83, each of which connects a source of positive potential 84 thereo. Although the key switches 82 and 83 are shown as conventional key switches any other switching mechanism such as a transistor or the like may be employed instead.

The circuit 17 includes an output line 85 connected to the terminal 65 of the unit 12 and a timing capacitor 86 connected between that line and a plane of reference p0- tential or ground. A resistor 87 for controlling the attack time is connected between the line and the input from the switch 82.

Also connected to line 85 is one side of a resistor 88 whose other side is connected to the movable blade of a three contact switch 90. The switch 90 is mechanically ganged to a second three contact switch 91. The movable blade of this switch 91 is connected in series through a diode 92 and resistor 93 to the input line of the circuit 17. The diode 92 is connected so as to allow conventional current ow essentially only through switch 91 when in the 91C position from battery 95 to battery 84 by way of resistor 93 and switch 82.

The fixed contacts of the ganged switches 90 and 91 are respectively designated 90A, 90B, 90C and 91A, 91B, 91C. The switches 90 and 91 are ganged so that they make contact with either contacts 90A and 91A, contacts 90B and 91B or contacts 90C and 91C. The contact 90A is grounded while the contacts 91A and 91B are electrically isolated. The contacts 90B, 90C and 91C are connected together and to a source of positive potential 95.

With the blades of the switches 90 and 91 in contact with the terminals 90A and 91A the resistance 88 is in parallel with the capacitor 86 but the circuit branch comprising resistor 93 and diode 92 is isolated and thus ineffective. With the blades in contact with terminals 90B and 91B the branch including resistor 93 and diode 92 remain isolated but the resistance 88 is connected to the positive potential source 95. When the blades are in contact with therminals 90C and 91C the resistor 88 remains connected to the source 95 and the branch with diode 92 and resistor 93 is also conected thereto.

Referring now to FIG. 2, one construction of the synthesizers 30 is there ilustrated. This includes effectively four metal-oxide-silicon field effect transistors (MOS FET) 101, 102, 103 and 104. The MOSFETs are of the P channel type and are operated in enhancement mode. The MOSFET is also known as an insulated gate lield effect transistor (IG FET) or sometimes simply as a metal oxide semiconductor (MOS).

A MOSFET when constructed as a discrete unit includes four elements: a gate (G), a drain (D), a source (S) and a substrate (Sub).

The four MOSFET elements 101, 102, 103, 104 of each synthesizer 30 have their gates electrically in common and coupled as symbolized by the lines 105, to the keying input 35. The MOSFETs also have their substrates electrically in common as symbolized by the lines 106. And as symbolized by the lines 107 these MOS FETS 101-104 have their drains electrically in common. The sources of the MOSFETs 101, 102, 103, and 104 are respectively coupled to the inputs 34, 33, 32 and 31 as symbolized by the lines 111, 112, 113, and 114.

In accordance with a feature of the invention the source-drain effective resistances of the MOSFETs 101 and 104 are of a specific relationship. That is, the sourcedrain resistance of the MOSFETS 101, 102, 103, and 104 when in the conductive or on state is related approximately in the ratio 1:2:4:8. Some adjustment needs to be made in practical circuits to accommodate load and source resistances and so forth as will be appreciated. For example, if the source-drain resistance of MOSFET 101 is 20K ohms, that of MOSFET 102 is about 40K ohms, that of MOSFET 103 is about 80K ohms, and that of MOSFET 104 about 160K ohms. The object of this is to approximate a Fourier series of harmonics for a sawtooth wave. That is, 100% fundamental, 50% second harmonic, S31/3% third, 25% fourth, 20% fifth, etc. With four inputs as shown, the missing harmonies are only the sixteenth and multiples thereof. The general case for the rst missing harmonic is 2n where n is the number of inputs.

All the MOSFETs 101-104 have a common substrate as is indicated in FIG. 2 by the use of the abbreviation Sub. adjacent the chassis symbol 115. It is, therefore, possible to fabricate many of the circuit elements unitary physical entities as the many common connections will suggest. For example, the keying input 35, all the lines 105 and the gates of MOSFETS 101-104 may be integrated. Furthermore, the entire unit 12 shown enclosed in dotted lines in FIG. 1 is preferably made as an integrated circuit on a common substrate.

The substrate is maintained at a positive potential above ground by a positive potential source 120 connected to a suitable substrate terminal 121 as illustrated in FIG. 1. As is common practice with such integrated circuits, Zener diode protection, such as symbolized by the diodes 125 and 126 connected respectively between the keying input terminals `65, 70 and the substrate, is provided. These Zeners or their equivalents are preferably built into the unit, but are not active during normal circuit operation.

In overall operation the above described circuitry functions to both synthesize from the input square Wave signals and to key a stairstep-sawtooth waveform such as the waveform 130 shown adjacent output terminal 76, at the output terminals 76-80 in response to the depression of a key such as the key 82 or the key 83. Furthermore, the type of envelope response to a single depression of one of the keys such as keys 82 or 83 can be varied. A long response or slow decay of the keyed signal, or a medium response or a fast decay may be achieved for instance.

As one concrete example, the square wavefrequencies of the unit 12 input terminals 20F420A can be as stated above 740 Hz., 3520 Hz., 1760 Hz., 880 Hz., 440 Hz., and 220 Hz., respectively. These input signals being of the order of four volts, peak to peak, the following values may be employed.

Capacitor 86-0.1 microfarad Resistor 87-22K ohms Resistor 88-10M ohms Resistor 93-33K ohms The voltage source 84 should be at approximately seven volts negative, and the source 120 at approximately six volts positive.

Referring to FIG. 3 an alternate construction for the synthesizer 30 of FIGS. 1 and 2 (Here designated 30 to distinguish it from the construction of FIG. 2) is illustrated. Again this arrangement can be achieved by discrete elements, but is preferably provided as an integrated circuit.

The synthesizer 30 includes a four emitter NPN type transistor 130 having a single base coupled, as illustrated by line 131, to the keying input 35 and a single collector coupled, as illustrated by the line 132, to the output terminal 36. Each of the four emitters of the transistor 130 is coupled through a resistance 133, 134, 135 or 136 to, respectively, the inputs 31, 32, 33 and 34.

The resistances 133, 134, 135, and 136 are realted in value in the ratio 8:4:2:1. That is, value of the resistance 135 is twice that of resistance 136, and that of resistance 134 is four times that of resistance 136, and that of resistance 133 is eight times that of resistance 136. As an example, representative values for these resistances are:

Ohms Resistance 136 2, 000 Resistance 135 4, 000 Resistance 134 8, 000

Resistance 133 16, 000

In this construction of the unit 12 the values for the keying response circuits 17 and for the potential source 83 of the combined circuit of FIG. 1 are different, although the basic arrangement is the same. In the case of the unit 12', the following values would be representative.

Capacitor 86-3 microfarads Resistor 88-220K ohms Resistor 87-2,200 ohms Resistor 93-3,300 ohms The voltage source 84 is a positive three volt direct current source, rather than the negative seven volts employed with the MOSFET approach. The size of the capacitor 86 should be, unlike that of the MOSFET unit 12, increased in capacitance depending upon the number of synthesizers 30 keyed by the circuit 17 or 19.

In operation the synthesizer 30 functions to synthesize a stairstep-sawtooth waveform such as the waveform 137 at its output 36 from square wave inputs such as 138-141, at its inputs 31-34 in response to a keying signal at its keying input 35. That is, a rise in its base potential renders the transistor conductive allowing the signals Present at its emitters to be translated and combined at its collector.

Referring now to FIG. 4 an alternative construction for the unit 12 of FIG. 1 is there illustrated and designated 12. This nut 12 differs mainly in the provision of buffer semiconductor elements 120A4120F one of which is coupled between the respective ones of input terminals 20A-20F and the synthesizers 30A to 30E.

The elements 120A-120F are of the positive channel MOSFET type and have their gates coupled to their respective input terminals 20A-20F as symbolized by the lines 140A-140F and their sources coupled in common to the substrate as indicated by the line 141. The drains, designated 2A-200F of the MOSFETS 120A-120F are in FIG. 4 coupled to the synthesizers 30 in the same manner as the terminals 20A-20F were in the unit 12 of FIG. 1.

Zener diode protection or its equivalent such as that depicted in FIG. l should, as a matter of course be understood to be employed. As this does not affect the normal operation of the unit 12, and is well known, it has not been depicted. A

In overall operation the unit 12 of FIG. 4 which preferably has synthesizers 30 constructed as illustrated in FIG. 2, functions in the same manner as the unit 12 of FIG. 1, except that the performance is improved by the provision of the buffer MOSFETS 120A-120F.

As should now be apparent a new and improved keyersynthesizer unit and keyer-synthesizer has been described which is capable of many applications. The keyed synthesizers 30 provide for both economy of manufacture and conservation of parts and space by combining the synthesis and keying functions in a unique circuit which can be comprised principally of several identical integrated circuit elements.

It should be noted that while the circuitry of the five synthesizers which comprise the unit 12 is preferably integrated and formed at one time, it is possible to obtain many of the benets of the present invention by employing discrete circuit elements. Also, as many such units normally will be used in an electronic organ or similar electrical musical instrument, it is convenient to form several of the units 12 simultaneously upon a single substrate element. In fact, it is presently believed that such an integrated package of several units having common elements, such as the substrate, is the most advantageous manner of practicing the invention.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A musical instrument keyer-synthesizer for synthesizing and controlling a complex electrical output musical signal from a plurality of relatively simpler electrical input musical signals upon demand comprising: semiconductor means having a common gate element, a common output element, and a plurality of individual input elements, circuits individually coupled to said input elements to receive individually the plurality of input signals, said semiconductor means being normally nonconductive but responding to a predetermined potential change at said gate to allow current ow simultaneously from said plurality of input circuits through said semiconductor means to said common output element to cornbine said plurality of input signals into a mixed signal at said output, said individual input circuits including scaled individual impedance elements for relatively scaling the levels of the individual input signals comprised in the mixed output, and means under the control of an operator connected for effecting said gate element potential change upon demand.

2. A keyer-synthesizer for synthesizing and controlling an electrical output signal from a plurality of electrical input signals as dened in claim 1 in which the individual signals impressed ou said individual inputs are octavely related square waves and the impedance scaling is such that the signal developed at said output in response to a potential change at said gate is a stairstep-sawtooth signal.

3. The keyer-synthesizer as called for in claim 2 in which the separate square wave input signals have fundamentals representing the fundamental, second harmonic, fourth harmonic and eighth harmonic, representative of the desired output and in which the impedance elements are scaled to produce at the output a mixed signal having the fundamental at substantially x value, the second harmonic at x/ 2 value, the third harmonic at x/ 3 value and the fourth harmonic at x/ 4 value.

4. The keyer-synthesizer as deiined in claim 3 in which said semiconductor means is of the MOSFET type, said inputs are at least four in number and the effective resistances of said inputs are related substantially as 5. The keyer-synthesizer as defined in claim 3 in which said semiconductor means is a multiemitter, common base and single collector transistor having at least four emitter inputs whose effective resistances are related substantially as 1:2:4:8

6. An integrated circuit keyer-synthesizer unit for synthesizing and keying five separate musical output signals comprising a substrate having elements thereon to provide ve separate semiconductor means each having a common gate element, a common output element and a plurality of separate input elements, circuit means connecting the input elements of a pair of said semiconductor means in parallel sets, means connecting said sets to individual sources of harmonically related square waves, circuit means connecting the input elements of a second pair of semiconductor means in parallel sets, means connecting the last said sets to individual sources of harmonically related square waves one octave lower than the sources connected to the rst said set, means connecting the input elements of the iifth semiconductor means to individual sources of harmonically related square waves one octave lower than the sources connected to said second set, comrnon keying circuit means connected to one of the gate elements of the first said pair, one of the gate elements of the second said pair and the gate element of the fifth semiconductor means, a second common keying circuit connected to the remaining gate elements of the semiconductor means in the first and second said pairs, and means for keying said separately keying circuits separately.

7. The keyer-synthesizer unit as defined in claim 6 in which said semiconductor means are all of the MOSFET type, said inputs for each semiconductor means are at least four in number and the effective resistances of said inputs to each semiconductor are related substantially as 1:2:4:8

8. The keyer-synthesizer units as defined in claim 6 in which said semiconductor means are all of the multiemitter, common base, single collector transistor type, said inputs to each transistor are at least four in number and the effective resistances of said inputs to each transistor are related substantially as 1:2:4z8

References Cited UNITED STATES PATENTS 2,498,337 2/1950 Kent SLi-1.22 3,291,886 12/1966 Tinker 84-1.01

W. E. RAY, Primary Examiner S. I. WITKOWSKI, Assistant Examiner Us. C1. X.R.

gygg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Parent No. 3,534, 144 Dated October 13, 1970 InventoL-(S) William C. Ring It is certified that error appears in the above-identified patent' and that said Letters Patent are hereby corrected as shown below:

Column 4, line +1, "thermnals" should be "terminals-- Column 5, line 42, "740Hz" should be 7040Hz.

Column 6, line 28, "nut" should be unit.

Signed and sealed this 20th day of April 1971.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. WLLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

